Many applications of solar energy are through its thermal effects. In these, solar radiation is absorbed by special surfaces and the energy converted to heat. The heat generated can then be used either directly, to provide for example domestic or industrial hot water, space heating or process heat; or the heat can be converted to mechanical energy (which can then be further converted to electricity) or to drive absorption cycle refrigerators. For the latter applications high temperature heat is an advantage since the efficiency of the processes is greatly improved.
Commercial flat plate collectors available today cannot provide sufficiently high temperature for the efficient conversion to mechanical energy or to drive absorption refrigerators. Methods are known for the production of high temperatures from solar energy. These use concentrating devices such as lenses or mirrors. Indeed some of the very highest temperatures on earth have been reached in such solar furnaces.
The main disadvantage of such devices for general application is the need for accurate tracking of the sun in its apparent motion through the sky. The higher the concentration (and therefore temperature) the more precise has to be the tracking mechanism.
For a number of applications of wide utility very high temperatures are not essential. Thus, for space heating and cooling, using absorption refrigeration cycles, moderate temperatures somewhat above the boiling point of water are sufficient. Also, special turbines exist which can run on relatively low heat sources. For such applications it is possible to dispense with high concentration and therefore with the need of tracking.